1. Field of the Invention
The present invention relates to a still operation of a washing machine, and more particularly, to a washing machine which includes an operation condition of the washing machine in correspondence with each of a plurality of stillness modes and operates according to the operation condition corresponding to any one selected from the plurality of stillness modes.
2. Discussion of the Related Art
In general, when dirty clothes are put into washing water, the clothes are washed by a chemical action of a detergent. However, if only the detergent is used, a washing time is long and the clothes may be damaged. Accordingly, in a washing machine, a mechanical action such as proper friction or vibration is applied to the clothes immersed in the washing water, for the purpose of improving a washing speed.
A drier is a mechanical device for drying wet laundry by hot air.
A washing machine is a device for processing laundry, which includes a washer, a drier, and dehydrator.
Recently, a consumer's request for the improvement and diversification of the capability of the washing machine is gradually increasing. A consumer's request for a still operation of the washing machine is also gradually increasing.
Consumers want a quite life. In particular, since there are frequent occasions when a washing machine is driven at night, a still operation is required.
A consumer may want or may not want a still operation. If a consumer wants a short operation time of a washing machine due to lack of time, a still operation may not be required.
However, a conventional washing machine is designed such that there is no room for selecting a stillness degree of an operation. Although a consumer wants a higher stillness degree of an operation, the washing machine should operate in a stillness mode set previously.
A consumer does not need to necessarily select the stillness degree of the operation, but a washing machine requires a variety of stillness modes. The stillness mode may vary depending on a condition.
For example, a dehydration operation of a conventional washing machine will be described with reference to FIGS. 1 and 2.
First, FIG. 1 is a flowchart illustrating a dehydration operation method of a conventional washing machine and FIG. 2 is a graph showing rotation speed (RPM) versus time in the dehydration operation method of the conventional washing machine.
In general, the dehydration function of the washing machine includes steps of disentangling laundry, evenly distributing the laundry, and detecting an unbalance amount (hereinafter, referred to as a UB amount). A drum stops or accelerates to perform a main dehydration mode according to the result of detecting the UB amount.
Now, a method of detecting the UB amount will be described with reference to FIGS. 1 and 2.
First, when a mode is switched to a dehydration mode, the rotation speed of the drum (not shown) in which laundry is contained increases and this state is maintained (S1).
Next, a degree to which the laundry is unevenly distributed in the drum, that is, the UB amount, is detected (S2).
For example, the UB amount is detected using a variation in rotation speed of a motor. That is, while rotating the motor by a predetermined dehydration algorithm, a position detection hall sensor mounted in the motor detects the rotation speed of the motor in a predetermined time period to measure a variation in rotation speed of the motor, and the UB mount is detected using a difference between a maximum value and a minimum value of the measured values. Since the method of detecting the UB amount is widely known, the detailed description thereof will be omitted.
Next, it is determined whether the UB amount is greater than an allowable value of a system, that is, a reference UB amount (S3).
If it is determined that the UB amount is greater than the reference UB amount, the dehydration operation is stopped in order to prevent the system from being damaged due to excessive rotation (S4) In contrast, if it is determined that the UB amount is less than the reference UB amount, the rotation speed of the motor increases and the main dehydration operation is performed (S5).
In the main dehydration operation, the drum rotates up to a maximum rotation speed.
Noise and vibration occur in the above-described dehydration operation of the washing machine.
In particular, noise or vibration varies depending on the condition of a floor on which the washing machine is installed. For example, in a case where the washing machine is installed on a wooden floor, the noise or vibration of the washing machine increases compared with a case where the washing machine is installed on a concrete floor.
Although the washing machine is installed on the same floor, a degree to which the noise or vibration is felt by a consumer varies depending on a use time period. The noise or vibration is felt to be larger during a quiet night than during the day.
Such a problem is not restricted to the dehydration operation and may be generated in a washing operation or a drying operation.
A principal factor for the noise or vibration may be related to the rotation speed of the drum. When the rotation speed of the drum increases in the washing operation, the drying operation or the dehydration operation, the noise or vibration increases.
That is, since the conventional washing machine is designed such that there is no room for selecting a stillness degree of an operation, a user feels inconvenience.